The ads will reportedly appear before certain videos begin playing.
The social media giant is to trial advertisements at the beginning of some of its videos at the start of next year.
"While News Feed will remain a powerful place for publishers and creators to grow and connect with their audience, over time we expect more repeat viewing and engagement to happen in places like Watch".
Facebook will fill the pre-roll inventory with any video ads that brands run on Facebook that are six seconds long and bought with the in-stream placement selected, according to a Facebook spokesperson. In August, it introduced Watch, a platform created to let users more easily watch videos within Facebook's mobile apps, TV apps and on computers.
The pre-roll move should prove popular among advertisers and content producers, while it remains to be seen if users will sit through ads before they can view Watch videos.
After resisting the urge to launch pre-roll ads on its network, Facebook is finally embracing the idea.
Starting in January, they won't be included in any videos shorter than 3 minutes, and the first ad won't pop up until at least a minute into whatever riveting content you're consuming. Video ads, in particular, have been a problem for Facebook, with research suggesting viewability on Facebook significantly trails industry averages.
If you too find yourself returning to Facebook for the videos, you might have come across an issue that causes just the live variety to lose audio. "Furthermore, across initial testing, satisfaction increased 18 percent when we delayed the first Ad Break placement", Angelidou-Smith and Bapna wrote.
One of the advertising changes announced by Facebook may also increase the time spent on the platform. Facebook has incentivized users over the past year to post more live videos, longer form videos and videos generally. The shift will apply to Facebook's News Feed and Watch's Discover tab and is likely to boost the reach and potential viewership of episodic series, such as the ones that Facebook is paying publishers to produce for Watch. There is a reason video game live streamers have begun considering Facebook as a viable alternative to the likes of Twitch and YouTube Gaming.